Insulated piston



P 1940- I o. G. SCHROM 2,214,891

INSULATED PISTON Filed Aug. 18, 1937 INVENTOR Oscar Gifichrom. I

/3 ATTORNEYS Patented Sept. 17, 1940 UNITED STATES PATENT OFFICE 4 Claims.

My invention relates to pistons for internal combustion engines; it is particularly desirable for use in those types of Diesel and other internal combustion engines in which exceedingly high pressures and temperatures are developed.

In such engines it has been found useful to make the pistons of some very light metal such as aluminum, or alloys of aluminum, in order to reduce their weight. In some modern practice t pressures and temperatures have gone so high that the point has been reached where it has been found that these light metals tend to break down. To minimize this difficulty it has been found desirable to cover the aluminum piston with a cap of some special heat-resisting material, such as stainless steel with high chromium and nickel content, for example, which is capable of enduring the high temperatures and pressures without serious distortion. The problem arises of mechanically fastening the cap to the piston; it has been found that if the cap is riveted to the piston the rivets tend to work loose, on account of the unequal heat expansion of the two metals. 'It has been suggested that th cap and piston s be bolted together, using spring washers under the bolts, but there is no spring washer which will retain its elasticity under theaction of the temperatures which are often used. One object of my invention is to provide a construction in a which the cap is so shaped that it can be attached to the piston without the use of spring washers and in which the uneven expansion due to temperature will :be compensated. Another object is to reduce the flow of heat from the cap a to the other'parts.

In the single figure of drawings attached to this I specification, I is the piston, which, as stated above, should be made of aluminum, aluminum alloy or other light material; 2 is the opening for the wrist pin; 3, 3, 3, are grooves for rings; 4 is the cap, preferably made of stainless steel, and constructed in hollow form, both to secure the flexibility described below and also to afford an air space 5, which is closed by a disc 6. The lower end of the cap is threaded as shown at I, and the cap is fastened in place on the piston by a nut 8, working on the thread I and coming into contact with the lower face 9' of the head of the piston. l0, ID, are notches in the nut which 50 cooperate with a special wrench.

A smooth face or seat is machined on the upper side of the piston head near the periphery as shown at H, and a similar smooth face I! is machined on the lower side of the cap. These two faces are held in contact by the nut 8 act- (Cl. cos- 9) ing on face 9. Adjacent the seat I I is an internal shoulder 13 which is engaged by a short cylindrical surface It on the cap whereby the cap is maintained in accurately centered relation to the piston. A narrow but deep annular groove l5 outwardly from the two machined faces H and I2 forms an air space which restricts the flow of heat towards the packing rings 3. The cap and piston are so shaped as to afford an air space I6 between them, and the lower end of the cap is prevented from being distorted towards one side or the other, by means of a, narrow lip ll formed, for example, on the piston adjacent the lower face 9. The fit between the cap and this lip is a loose fit.

The upper part of hollow circular cap 4 comprises a central portion l8 (preferably dome shaped), forming the upper wall of central chamher 5, and a heavier circular section l9 at the circumference. This heavy ring-shaped section at the outer edge of the heat plate of the piston enables the cap to resist distortion due to the heat and also due to the explosion pressure within the cylinder. The upper part of the piston cap is, therefore, substantially rigid, while the lower part possesses the necessary degree of elasticity or flexibility, which is one object of my invention.

It will be seen that the lower walls of the central chamber 5 of the cap converge downwardly like the frustum of an inverted hollow cone and then are carried still farther downwardly in the form of a tubular extension smaller than the largest diameter of the chamber 5. This construction is particularly useful for affording flexibility such as to allow elastic distortion of the piston without unduly straining the metal of which it is composed, to such an extent that when the nut 8 is tightened the cap is capable of such elastic yielding between the bearing point I! and the point 9 at which the nut makes contact with the piston that sufilcient pressure can be exerted by the nut to produce a good, tight joint at I2, and any unequal expansion or contraction of the cap and piston can be taken care of by the elastic movement in the body of the cap itself, plus whatever elastic movement the piston may perform,-and there is no serious tendency for the parts to work loose because of expansion and contraction.

Coming now to the means by which I reduce 50 ing rod and wrist pin bearing are located. Also 55 it will be seen that the connecting rod space is not occupied as it would be by the use of bolts, nuts and spring Washers to hold the piston cap in place. Heat insulation is further secured by the air space l6 described above, which aids particularly in keeping heat away from the ring grooves 3, 3, 3, and therefore from the rings and from the lubricant. In this manner I am able to provide two air spaces arranged in series in the principal path of heat flow from the upper part of the cap to the piston.

The pressure exerted by the explosive mixture in the cylinder on the top-of the piston cap is transmitted in a very straight line through the body of the piston to the wrist pin bearing, thereby imposing the minimum possible mechanical strain upon the metal.

I claim:

Y 1. A piston having a cap seat and a depression radially inwardly of the cap seat, said depression having an axial opening in the bottom thereof, a cap comprising a portion seated on said cap seat, an extension extending axially through said axial opening and a portion connecting said extension with the portion which seats on said cap seat, said connecting portion being distortable and when not under distorting stresses conneoting with said extension axially-outwardly from the bottom of said depression and having its axially-inner surface extending from said extension spaced from the axially-opposite portion of the piston for a substantial part of the distance towards said cap seat, and means carried by said extension for fastening said cap to the piston,

said cap being fastened to the piston by said fastening means with said distortable portion thereof distorted axially inwardly, said inward distortion elastically securing the cap to the piston and compensating for difierences in expansion between the piston and the cap.

2. A piston having a cap seat and a depression radially inwardly of said seat, said depression having an axial opening in the bottom thereof, a cap comprising a portion seated on said cap seat, anextension extending through said axial opening and having one end extending into said depression axially-outwardly of said opening and a portion connecting said end of the extension with the portion which seats on said cap seat, and means carried by the other end of said extension for fastening the cap to the piston, said connectpensate for differences in expansion between the piston and the cap and said extension being movable axially within said opening to facilitate such compensation.

3. A piston having a can seat and a depression radially inwardly of the cap seat, a cap having a central chamber and comprising a portion seated on said cap seat, an axially extending securing portion axially-inwardly of said cap seat adapted to cooperate in securing the cap to the piston and a distortable portion connecting said securing portion to the portion which seats on saidcap seat, and means for fastening said securing portion to the piston to retain'the cap in place, the axially-inner surface of said distortable portion where it joins the radially-outer surface of said securing portion and the radiallyouter surface of the axially-outer portion of said.

securing portion where it joins said distortable portion, 'respectively, being spaced from the axially-opposite and radially-opposite portions of the piston for a substantial distance along said surfaces, whereby there is provided an elastic structure to compensate for differences in ex-, pansion between the piston and the cap.

4. A piston having a cap seat spaced inwardly..- from the periphery thereof and a depression.

radially inwardly of the cap seat, said depression having an axial opening in the bottom thereof, a cap having a central chamber and comprising a portion seated on said cap seat, a portion ex-' tending beyond said cap seat and overlying and spaced from the head of the piston to provide an annular air space outside of the contact faces of the cap and piston, a tubular extension extending axially through said axial opening and axiallyinwardly-converging, distortable Walls connect-- ,surfaces, whereby there is provided an elastic structure to compensate for differences in expansion between the piston and the cap.

OSCAR G. SCI-IROM. 

